1. Field of the Invention
The present invention relates to a focus adjustment apparatus and method, and an image capturing apparatus and, more particularly, to a focus adjusting technique by a focus adjustment apparatus used in an image capturing apparatus such as a digital still camera and video camera.
2. Description of the Related Art
Conventionally, as a method of adjusting a focal point on an object by driving a focus lens in a digital still camera or the like, an AF (Auto Focus) method of automatically performing a focusing operation using an image signal obtained from an image sensor such as a CCD is used. When this AF method is used, processes such as photometry processing for AE (Auto Exposure) control, AE control, WB (White Balance) control, and a change to signal read-out control of the image sensor suited to the AF control are executed in response to, for example, a photographing preparation instruction operation such as pressing of a shutter button to a half-stroke position. After these processes, the AF control based on the aforementioned AF method is executed.
In one related art using this AF method, the photometry processing before the AF control and scan control of the focus lens to an operation start position of the AF control are parallelly executed to shorten an AF time lag (for example, see Japanese Patent Laid-Open No. 2006-254191). In another related art, an AF time lag is shortened by determining the operation start position of the AF control, the scan speed of the focus lens, and a focus detection area based on the AF evaluation value acquired during a scan of the focus lens to an AF scan start position (for example, see Japanese Patent Laid-Open No. 2012-093409).
However, with the method of Japanese Patent Laid-Open No. 2006-254191, since the photometry processing is executed during a scan of the focus lens to the operation start position of the AF control, a luminance variation due to the scan of the focus lens affects the photometry precision. On the other hand, with the method of Japanese Patent Laid-Open No. 2012-093409, the scan control of the focus lens to the operation start position of the AF control is not parallelly executed with photometry processing, AE control, WB control, and the change to the signal read-out control of the image sensor suited to the AF control. For this reason, when an AF evaluation value acquired during a scan to the operation start position of the AF control cannot be effectively used, a scan time of the focus lens is wasted.